The present invention relates to tracheal tubes and, more particularly, to tracheal tubes of the type embodying a cuff for effecting a seal between the tube and a trachea.
As is well known in the art, tracheal tubes are commonly inserted into a person's trachea for various purposes; for example, to enable the person to breathe, or to enable intermittent positive pressure ventilation of the respiratory tract to be carried out. The tracheal tube of the present invention is of the cuffed type and is particularly well adapted for the mechanical ventilation of the respiratory tract, especially where high ventilating pressures are utilized.
Tracheal tubes, as that term is used herein, may be of different types, such as, for example, orotracheal tubes, nasotracheal tubes and tracheostomy tubes. Typically, such tubes include a main body portion in the form of an elongated tube made of flexible material such as, rubber polyvinylchloride, or they may be stiff or rigid, made of material such as stainless steel.
There are two types of cuffed tracheal tubes commonly used in the art. One type of tracheal tube is characterized by a cuff including a cover filled with resilient material, with the cover normally being disposed in expanded position and being collapsed by applying a vacuum thereto during insertion or removal of the tube into or from the trachea. A tracheal tube of this general type is described in U.S. Pat. No. 3,640,282, issued to Kamen and Wilkinson on Aug. 6, 1970, and forms the subject matter for my co-pending application Ser. No. 291,322, entitled Tracheal Tube and filed Aug. 10, 1981.
A second type of tracheal tube is characterized by a cuff which is not filled with a resilient material. Such cuffs are uninflated or deflated in condition. With such devices, after the intubation device has been inserted into the trachea, the cuff is inflated like a balloon, by feeding air or other working fluid thereinto at a positive pressure to thereby expand the cuff into engagement with the inner wall of the trachea. However, it has been found that such devices have several inherent disadvantages, the primary disadvantage being that they commonly cause injury to the trachea, causing lesions such as tracheal stenosis, tracheal malacia and localized erosion, particularly if it is necessary for the tube to remain in the trachea for prolonged periods of time.
Current techniques of mechanical ventilation of the respiratory tract often employ relatively high positive air pressure. This pressure is highest at the peak of the inspiratory phase and lowest at the termination of the expiratory phase. The human trachea is elastic and stretches increasing in diameter, in part, with increasing pressure in the respiratory tract. The degree of elasticity of the trachea varies and is dependent upon a number of factors, the majority of which cannot be controlled during mechanical ventilation.
Mechanical ventilation techniques and tracheal elasticity create a problem for cuffed endotracheal tubes to overcome. If the cuff is of the air-filled type, the volume of air required to prevent leakage of ventilation gases at peak inspiratory airway pressure exceeds the volume of air needed in the cuff during expiration. The cuff must be overinflated during expiration to prevent leakage during inspiration. The result in many instances is a progressive stretching of the trachea with ultimate tracheal injury.
On the other hand, when the cuff on the tracheal tube is of the expandable-material filled type, such as, for example, the type disclosed in the aforementioned Kamen and Wilkinson U.S. Pat. No. 3,640,282, the cuff contents exert progressively less force against the tracheal wall as the elastic trachea's volume is expanded at peak inspiratory pressure. If this expansion of the elastic trachea is of sufficient magnitude, the result is an inadequate seal between the cuff and the trachea.
Heretofore, in an attempt to insure the proper seal between the trachea and a cuffed tracheal tube during mechanical ventilation and to minimize or prevent tracheal injury, cuff inflator machines have been used. These machines either attempt to vary the cuff volume and pressure synchronously with a companion ventilating machine or to maintain a constant cuff pressure while varying the cuff volume during the changing requirements of a complete inspiration/expiration cycle. These machines have several disadvantages, among which are that they are expensive and are subject to the maintenance and calibration problems inherent to precise machinery.